The present invention relates to a liquid crystal device for use in a liquid crystal display device, an optical shutter array, etc., and more particularly to a ferroelectric liquid crystal device having improved display and driving characteristics, because of improved initial alignment or orientation of liquid crystal molecules.
Clark and Lagerwall have proposed the use of a liquid crystal device having bistability (Japanese Laid-Open Patent Application No. 107216/1981, U.S. Pat. No. 4,367,924, etc.). As the bistable liquid crystal, a ferroelectric liquid crystal having chiral smectic C (SmC*) phase or H (SmH*) phase is generally used. The ferroelectric liquid crystal has bistability, i.e., has two stable states comprising a first stable state and a second stable state, with respect to an electric field applied thereto. Accordingly, different from the conventional TN-type liquid crystal in the above-mentioned device, the liquid crystal is oriented to the first stable state in response to one electric field vector and to the second stable state in response to the other electric field vector. Further, this type of liquid crystal very quickly assumes either one of the above-mentioned two stable states in reply to an electric field applied thereto and retains the state in the absence of an electric field. By utilizing these properties, essential improvements can be attained with respect to the above-mentioned difficulties involved in the conventional TN-type liquid crystal device.
In order to provide a uniform orientation or alignment characteristic to a ferroelectric liquid crystal in the above described type of device, there has been known to apply a uniaxial alignment treatment onto a substrate surface. More specifically, the uniaxial alignment treatment includes a method of rubbing a substrate surface with velvet, cloth or paper in one direction, or a method of obliquely depositing SiO or SiO.sub.2 on a substrate surface.
By applying an appropriate uniaxial alignment treatment to a substrate surface, a specific bistable condition has been provided as an initial alignment characteristic. Under such an initial alignment condition, however, there have been observed practical problems such as poor contrasts and low light-transmittances during optical modulation tests carried out by using polarizers arranged in cross nicols in combination with the device.
More specifically, in a ferroelectric liquid crystal device of the type described above, a state wherein molecules of a liquid crystal (hereinafter sometimes abbreviated as "LC") are twisted from an upper substrate to a lower substrate in an LC molecular layer (twist alignment state) as shown in FIG. 21 is readily developed rather than a state wherein LC molecules are aligned in parallel with each other in an LC molecular layer (parallel alignment state) as shown in FIG. 22. Such a twist alignment of LC molecules leads to various disadvantages for a display device such that the angle formed between the LC molecular axes in the first orientation state and the second orientation state (tilt angle) is apparently decreased to result in a decrease in contrast or light transmittance, and overshooting occurs in the response of the LC molecules at the time of switching between the orientation states to result in an observable fluctuation in light transmittance. For this reason, it is desired that the LC molecules are placed in the parallel alignment state for a display device.